The present invention relates to an automatic balance device for disk, especially to an automatic balance device for disk, which comprises rolling beads of different sizes.
The conventional CD-ROM driver, as shown in FIG. 1, mainly comprises a base 10, a stage 11, a pick-up head 12, a spindle motor 13 and a turntable 14. The stage 11 is mounted on the base 10 through a plurality of flexible supports 15. The pick-up head 12 and the spindle motor 13 are placed on the stage 11 and the turntable 14 is fixed on top of the spindle motor 13. An optical disk 16 is mounted on the turntable 14 and is clamped by a clamping chassis 17. The turntable 14 is driven to rotate by the spindle motor 13, and the disk 16 on the turntable 14 is also rotated for accessing data thereon.
In order to reduce vibration and noise for a disk with unbalanced mass, the conventional CD-ROM driver is generally equipped with automatic balance devices. The automatic balance devices are classified as magnetic type and non-magnetic type.
As shown in FIG. 2, the non-magnetic type automatic balance devices for CD-ROM driver comprises a plurality of rolling beads 18 within the turntable 14 or the clamping chassis 17 and of the same size. The plurality of rolling beads 18 are functioned to compensate the imbalance force of the disk 16. However, when the disk starts to rotate, the rolling beads 18 are rolled toward the same orientation of the mass center of the disk with unbalanced mass. Therefore, the disk with unbalanced mass will have larger angular momentum when. beginning to rotate. This is the first drawback of the non-magnetic type automatic balance devices for CD-ROM driver. When the rotation angular frequency of the disk 16 exceeds the natural frequency of the composite structure of the stage 11 and the flexible supports 15, theoretically the rolling beads 18 will be rolled toward direction opposite to the mass center of the disk with unbalanced mass. However, the rolling beads 18 is subject to large frictional force due to large centrifugal force thereof. The rolling beads 18 have not sufficient kinetic energy to reach the designed position for eliminating the imbalance force of the disk 16, and the vibration and noise problems are worsened. This is the second drawback of the non-magnetic type automatic balance devices for CD-ROM driver.
As shown in FIG. 3, the magnetic type automatic balance devices for CD-ROM driver comprises a plurality of rolling beads 18 of same size and a magnetic piece 19 within the turntable 14 or the clamping chassis 17. The plurality of rolling beads 18 are functioned to compensate the imbalance force of the disk 16. The conventional magnetic type automatic balance devices for CD-ROM driver can be of dual-pole configuration or quadruple-pole configuration, as shown in FIGS. 4 and 5, respectively. When the disk starts to rotate, the rolling beads 18 are attracted by the magnetic piece 19 and not rolled toward the same orientation of the mass center of the disk with unbalanced mass, thus preventing worsened vibration and noise. When the rotation angular frequency of the disk 16 exceeds the natural frequency of the composite structure of the stage 11 and the flexible supports 15, the rolling beads 18 will be released from the magnetic piece 19 and rolled toward direction opposite to the inclined direction of the disk with unbalanced mass. However, the rolling beads 18 are of the same size, those rolling beads 18 will be released at the same time. If the rolling beads 18 are released to wrong positions, the rolling beads 18 cannot move to proper positions for eliminating the imbalance force of the disk 16. The rolling beads 18 have considerable frictional force with respect to the turntable 14 due to the large centrifugal force thereof. The rolling beads 18 will have no chance to gain energy to move to proper positions for eliminating the imbalance force of the disk 16.
It is the object of the invention to provide an automatic balance device for disk, by which the vibration and noise of the disk can substantially be eliminated.
To achieve the above object, the present invention provide an automatic balance device for disk, which comprises a plurality of rolling beads of different sizes and a magnetic piece within the turntable or clamping chassis of the CD-ROM driver. The rolling beads of different sizes will be released from the magnetic piece at different rotating speed of disk. Therefore, the rolling beads with larger weight are first released from the magnetic piece and then bumped by the rolling beads with smaller weight, which are released from the magnetic piece at later time. The rolling beads with larger weight can be moved to desired position to counteract the imbalance force of the disk.